Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$229.83	11.347%	$255.9088	$255.91	$255.90	$255.90
Purchase #2	$121.29	9.848%	$133.2346	$133.23	$133.25	$133.20
Purchase #3	$136.99	4.554%	$143.2285	$143.23	$143.25	$143.20
Purchase #4	$244.78	3.486%	$253.313	$253.31	$253.30	$253.30
Purchase #5	$179.89	11.192%	$200.0233	$200.02	$200.00	$200.00
Purchase #6	$79.90	3.256%	$82.5015	$82.50	$82.50	$82.50
Purchase #7	$19.92	4.212%	$20.759	$20.76	$20.75	$20.80
7 purchase totals =	$1,012.60		$1,088.9687	$1,088.96	$1,088.95	$1,088.90